Charge
transfer at the interface between single-walled carbon nanotubes
(SWCNTs) of distinct chiral vectors and fullerenes of various molecular
weights is of interest both fundamentally and because of its importance
in emerging photovoltaic and optoelectronic devices. One approach
for generating isolated, discretized fullerene–SWCNT heterojunctions
for spectroscopic investigation is to form an amphiphile, which is
able to disperse the latter at the single-SWCNT level in aqueous solution.
Herein, we synthesize a series of methanofullerene amphiphiles, including
derivatives of C<sub>60</sub>, C<sub>70</sub>, and C<sub>84</sub>,
and investigated their electron transfer with SWCNT of specific chirality,
generating a structure–reactivity relationship. In the cases
of two fullerene derivatives, lipid–C<sub>61</sub>–polyethylene
glycol (PEG) and lipid–C<sub>71</sub>–PEG, band gap
dependent, incomplete quenching was observed across all SWCNT species,
indicating that the driving force for electron transfer is small.
This is further supported by a variant of Marcus theory, which predicts
that the energy offsets between the nanotube conduction bands and
the C<sub>61</sub> and C<sub>71</sub> LUMO levels are less than the
exciton binding energy in SWCNT. In contrast, upon interfacing nanotubes
with C<sub>85</sub> methanofullerene, a complete quenching of all
semiconducting SWCNT is observed. This enhancement in quenching efficiency
is consistent with the deeper LUMO level of C<sub>85</sub> methanofullerene
in comparison with the smaller fullerene adducts, and suggests its
promise as for SWCNT–fullerene heterojunctions.